Canadian oyster killing parasite isolated

Some tiny, elusive parasites that have plagued oysters from British Columbia to California have been detected and identified for the first time.

The parasite was first identified in 1960, at Henry Bay on Denman Island. It has, however, taken over fifty years for researchers to capture it. The parasitic infection is known as Denman Island disease and it is caused by Mikrocytos mackini, a parasite that infects mainly Pacific oysters, and leads to unsightly yellow-to-green lesions or pustules, and eventually to death. Infected oysters die at a high rate and they do not ripen for spawning.

The difficulty in capturing the parasite related to the fact that the parasite lives inside the oyster's cells and it has hitherto proved impossible to grow and study in a laboratory. Oyster is a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. Many are edible and the oyster trade around British Columbia represent a major part of the local economy.

Now that the parasite has been isolated it appears similar to a group of amoebae called Rhizaria. The parasites die when exposed to oxygen and cannot survive for long periods away from the oyster shell. It is hoped that the isolation and improved knowledge about the parasites will form the basis of a means to eliminate the diseases.

Talking to the Vancouver Sun, Roberta Stevenson, executive director of the B.C. Shellfish Grower’s Association, welcomed the UBC research, said: “By no means is (Denman Island) disease a threat to our industry”, adding that the industry had robust controls in place.

The identification of the parasites was undertaken by University of British Columbia researchers. The findings have been published in the journal Current Biology.